1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic recording apparatus. In particular, the present invention relates to a magnetic recording medium and a magnetic recording apparatus based on the perpendicular magnetic recording system.
2. Description of the Related Art
In response to the development of the advanced information society, the needs are overwhelmingly increased for the realization of the large capacity and the high density of the information-recording apparatus. A magnetic recording apparatus is known as one of the information-recording apparatuses which respond to such needs. The magnetic recording apparatus is used as the large capacity recording apparatus including, for example, large scale servers, parallel type computers, personal computers, network servers, movie servers, and mobile PC's. The magnetic recording apparatus includes a magnetic recording medium on which information is recorded, and a magnetic head which records and reproduces information on the magnetic recording medium. The magnetic recording medium includes a disk-shaped substrate on which a ferromagnetic thin film such as cobalt alloy is formed as a recording layer, for example, by the sputtering method. A protective layer and a lubricant film are formed on the recording layer in order to enhance the sliding resistance and the corrosion resistance.
As the large capacity of the magnetic recording apparatus is progressively realized, it is advanced to improve the recording density of the magnetic recording medium by recording fine and minute recording magnetic domains in the recording layer of the magnetic recording medium. The perpendicular magnetic recording system attracts the attention as a method for finely recording the recording magnetic domains. In the perpendicular magnetic recording system, the magnetic recording is performed by forming magnetic domains having perpendicular magnetization in the recording layer by using the magnetic recording medium having the recording layer which exhibits the perpendicular magnetization. In the case of the perpendicular magnetic recording system as described above, the recording density of the magnetic recording medium can be increased, because fine and minute magnetic domains can be formed in the recording layer.
In the magnetic recording medium based on the perpendicular magnetic recording system, a layer (hereinafter referred to as “soft magnetic back layer” or “back layer”), which is formed of a soft magnetic material, is provided between the substrate and the recording layer. Accordingly, it is possible to converge and focus the magnetic field to be applied to the recording layer when information is recorded. It is possible to perform the recording on the magnetic material having higher magnetic anisotropy.
A technique has been hitherto suggested (see, for example, Japanese Patent Application Laid-open No. 2003-45014, p. 3, FIGS. 1 and 3 to 7), in which an in-plane magnetized film is provided between the back layer and the perpendicular magnetized film (recording layer) to reduce the noise caused by the disturbance of magnetization due to the interaction between the back layer and the perpendicular magnetized film.
In the case of the magnetic recording medium suggested by Japanese Patent Application Laid-open No. 2003-45014, the reverse magnetic field is generated in an in-plane magnetized film so that the magnetic pole, which is induced in the back layer by the perpendicular magnetized film, is counteracted by providing the in-plane magnetized film between the back layer and the perpendicular magnetized film. In particular, when the relationship of (saturated magnetic flux density of perpendicular magnetized film×film thickness)<(saturated magnetic flux density of in-plane magnetized film×film thickness) is satisfied between the perpendicular magnetized film and the in-plane magnetized film, the magnetic circuit, which is formed by the magnetic field of the perpendicular magnetized film, is closed by the in-plane magnetized film to give a structure in which any induced magnetic pole is not formed in the back layer by the leak magnetic flux of the perpendicular magnetized film. That is, in the case of the magnetic recording medium suggested by Japanese Patent Application Laid-open No. 2003-45014, the magnetic flux is refluxed between the in-plane magnetized film and the perpendicular magnetized film in order not to generate any induced magnetic pole in the back layer by the leak magnetic flux of the perpendicular magnetized film.
By the way, in the case of the magnetic recording apparatus based on the use of the magnetic recording medium of the perpendicular magnetic recording system, it is demanded to further improve the resolution defined by (reproduction output at high recording density/reproduction output at low recording density)×100 [%] in order to respond not only to the realization of the high recording density of information but also to a variety of ways of use and standards.